The short-term mechanisms and long-term impacts of even low-dosage transcranial stimulation are clinically unknown, and possibly unknowable in the near future. Indeed, the FDA withdrew its official guidance about so-called “limited output” specifications [36]. What constitutes “low-intensity” and “low-impact” (and so on) electromagnetic (EM) fields and forces, and what yields a “safe” dosage for neurons, brain areas, and the entire brain can only be speculative. Although the labeling of “limited output” EM sounds reassuring, nothing of proven clinical reality stands behind it. Matters such as “power densities” in living neuronal tissue are only approximately measurable. Since fewer noticeable side effects of a minor character have been reported where the maximum average current is less than 10 mA and a maximum peak current less than 30 mA for reasonably short durations (e.g., less than an hour per session), that has suggested itself as a “safety” standard, but higher amperes and durations have also been claimed to be “safe” enough under controlled research and clinical conditions. What constitutes genuine safety for large populations in uncontrolled settings remains a massive public health experiment.
Without consistent national or international statutes for non-medical devices, manufacturers can aim to satisfy various industry and academic guidelines. A prominent example is “Limited output transcranial electrical stimulation 2023 (LOTES-2023)” (Bikson et al. 2023) [36].
